Heart beats representing various states of a human are used as useful indicators in various fields such as health care, sleep state measurement, and medical treatment. There are mainly two methods for measuring heartbeats. One is a method using an electrocardiogram obtained from an electrode between two points flanking the heart and a reference electrode. The other is a method of capturing pulse waves due to blood flows through blood capillaries or the like synchronizing with the heartbeats.
It is difficult for ordinary healthy people to use the method using an electrocardiogram in their daily lives.
The pulse wave measuring method mainly includes a reflection type method and a transmission type method. Both the reflection type method and the transmission type method use a difference of light absorbing characteristics of intravascular substances. In the reflection type method, light-emitting elements and light-receiving elements are arranged side by side on a surface of an organism. Light is irradiated on peripheral blood vessels and an amount of reflected light is captured by the light-receiving elements (see, for example, JP-A-2000-107147 and JP-A-2002-360530). In the transmission type method, light-emitting elements and light-receiving elements are arranged to sandwich an organism to capture an amount of light transmitted through a blood vessel with the light-receiving elements.
Pulse waves are measured for various purposes such as autonomous nervous system measurement, prevention of life-style related diseases, and sleep state measurement. There is an advantage that pulse waves can be measured easily. However, since a measurement site is a fingertip, an earlobe, a wrist, or the like, the measurement of pulse waves is strongly affected by movement and is susceptible to disturbances such as movement in daily lives.
Therefore, the invention provides a pulse wave measuring apparatus and a method therefor that copes with a positional deviation of a sensor module and a change in a position of an artery on a real time basis and is robust against disturbances.